Make sure this testcase keeps crashing with -O3.

Recent optimization improvements made LLVM realize the store-to-null was
unavoidable, so it deleted all of main() and replaced it with 'unreachable'.
Because the body of main() no longer even contained a return instruction,
calling it caused random code to be ran instead. This happened to be the code
that links in the ModuleInfo on my machine, which then returned "successfully".

tests/mini/norun_debug11.d

@@ -28,6 +28,6 @@ void main()
 
     auto ci = c.classinfo;
 
-    int* fail;
+    int* fail = cast(int*) 1;
     *fail = 0;
 }